Worldwide production of ammonia exceeds 145 million metric tons per year. The Haber-Bosch process must be performed at high temperature and pressure using pure hydrogen, which is usually sourced from natural gas via steam reforming; hence ammonia production represents a significant contributor to climate change. Because of this, alternative methods for synthesizing ammonia are now of great scientific interest.
While the literature is still sparse, a number of electrocatalytic studies that produce NH3 directly via electroreduction of N2 and water or steam have been reported. Most studies on electrochemical production of ammonia are based on solid-state electrolytes at elevated temperature and pressure. Other studies have also been reported based on liquid electrolytes, such as organic solvents, ionic liquids, molten salts, aqueous electrolyte at elevated or ambient pressure, or fullerene electrodes with aqueous electrolyte. In these studies, transition metal complexes and materials are often exploited as the catalysts.
Aqueous electrolyte approaches promise simplicity and low cost, as the solvent water directly becomes the hydrogen source. However, aqueous electrolyte approaches suffer from competitive hydrogen evolution which limits overall efficiency. To date the highest reported Faradaic efficiency (FE) for an aqueous reaction under ambient conditions is 1.3%.
There is no report yet on alternative catalysts that allow one to abandon the conventional transition metal catalysts as a result of significant improvements of electrocatalytic performance. Thus, a more efficient and selective method for converting nitrogen into useful fuel products would represent a significant advance in the art.